Resistance alloys

ABSTRACT

RESISTANCE ALLOYS MADE ACCORDING TO THIS INVENTION HAVE HIGH ELECTRICAL RESISTIVITY AND ARE SUITABLE FOR MAKING RESISTANCE WIRE HAVING HIGH AND CONSTANT ELECTRICAL RESISTANCE. THE ALLOYS ARE PRIMARILY PALLADIUM/VANDIUM ALLOYS AND INCLUDE 0.5 TO 11% BY WEIGHT OF ONE OR MORE OF THE ELEMENTS GOLD, MOLYBDENUM OR ALUMINUM.

Feb. 9., 1971 v Filed May 10, 1968 J. J. NORREYS 3,561,956

RES I S TANCE ALLOYS 2 Sheets-Sheet 1 METAL 50w 50M. WIRES f N VENrOR (JOHN J E PHSOH Nd/ZRLYS CONTACT LOAD IN GRAMMES.

BASE BUN/20C:

Fgb. 9, 1971 I A 'J, NQRREYS 3,561,956

RESISTANCE ALLOYS Filed May 10, 1968 v 2 Sheets-Sheet 2 F/GZ CONTACT RES/STANCE VERSUS LOAD AGAINST A 62-5Au/275Cu/70Ag WIPE R.

ATTOQNE S United States Patent 3,561,956 RESISTANCE ALLOYS John Jephson Norreys, Duflield, Derby, Engiand, assignor to Johnson, Matthey & (30., Limited, London, England, a British company Filed May 10, 1968, Ser. No. 728,155 Claims priority, application Great Britain, May 11, 1967, 21,853/ 67 Int. Cl. C22c 5/00 US. Cl. 75-172 6 Claims ABSTRACT OF THE DISCLGSURE Resistance alloys made according to this invention have high electrical resistivity and are suitable for making resistance wire having high and constant electrical resistance. The alloys are primarily palladium/vandium alloys and include 0.5 to 11% by weight of one or more of the elements gold, molybdenum or aluminium.

This invention relates to resistance alloys, that is alloys which have high electrical resistivity and from which wire of high and constant electrical resistance can be made. More particularly the invention relates to resistance alloys containing palladium and vanadium.

It is known that palladium alloys containing up to 10% of vanadium have a high specific resistance and are ductile and moreover do not form surface oxide skins at room temperature. They are therefore suitable for use in precision resistance equipment where surface condition is important such as, for example, slide Wire potentiometers where minimum contact resistance is advisable.

The main disadvantage of palladium-vanadium alloys lies in the fact that the specific resistance is reduced and tends to vary in service when the alloy has been cold worked. The effects of the cold working may, however, be removed by annealing treatments.

According to the present invention palladium-vanadium alloys having high specific resistance and reduced temperature coefiicient of resistance include 0.5 to 11% by weight of one or more of the elements gold, molybdenum or aluminium. Preferably the alloys of the invention comprise a palladium-vanadium alloy having high specific resistance and reduced temperature coefiicient of resistance, the alloy comprising 74 to 98.5% by weight palladium, 1 to 15% by weight vanadium and balance apart from impurities consisting of one or more of the elements gold, molybdenum or aluminium.

It has been found that with such alloying additions, the palladium-vanadium alloys are not markedly subject to changes in their electrical properties due to cold work.

Such alloys have high specific resistance coupled with a lower temperature coefiicient of resistance and a lower susceptibility to changes in specific resistance and in temperature coefiicient of resistance than in the case of known alloys. Moreover these alloys have little tendency to form a surface oxide skin at room temperature and will thus maintain a low contact resistance when used in applications such as slide wire potentiometers.

These alloys are also capable of being worked down to the form of fine wire.

The following table (Table 1) shows the effect of the addition of small amounts of molybdenum, gold and aluminium on the specific resistance of palladium-vanadium alloys. The figures given show the percentage by weight of the additions:

TABLE 1 Pd-10 V- Id-10 V- Pd-lO V- Alloy Pd-lO V 2 Mo 5 Au 1 A1 Specific resistance:

Annealed uSZM 134 133 Work hardened OM" 114 120 128 1 240 Table 2 shows the effect of annealing on the characteristics of the known palladium-vanadium alloy and of an alloy according to the present invention containing 1% aluminium replacing part of the vanadium.

Small additions of molybdenum and gold both appear to stabilise the resistance of a palladium-vanadium alloy against cold work without thereby increasing its resistance. In particular We have found that gold appears to be effective both as a single addition and also when added in combination with aluminium.

One method of making a palladium-vanadium alloy according to the invention will now be described by way of example.

A charge consisting of 1800 gm. of palladium and gm. of vanadium, both in the form of grains together with 20 gm. of aluminium in the form of rod was melted in a vacuum-type furnace in an atmosphere of argon. The furnace was then evacuated to a pressure of 10* mm. Hg to remove remaining gas liberated during melting and argon was readmitted to a pressure of 400 mm. Hg before the melt was cast in a mould.

Samples of the sheet were taken for the purpose of analysis and, thereafter, the sheet was passed through a scalping machine to remove casting defects such as laps or folds. The scalped sheet was then homogenised by: heating to 1200 C. over a period of 2 to 3 hours; maintaining the sheet at 1200 C. for 4 hours and, finally, allowing the sheet to cool to room temperature over a period of 2 to 3 hours.

The homogenised metal was thereafter fabricated into wire and to avoid oxidation during fabrication any heating and cooling of the metal was carried out in an atmosphere of argon. Tests of contact resistance against load applied to a wiper in contact with the wire were thereafter carried out.

The accompanying diagram which, for convenience has been divided into parts A and B shows by way of example, a graphical relationship between contact resistance (measured in microhms) and load (measured in grammes) for wire having a composition 90 Pd:9 V= l Al using a Wiper made from alloy of 62.5 Au= 27.5 Cu=10 Ag.

From the graph, it will be seen that for wires made from base metals scattered results are obtained within the indicated boundaries. The scatter of the results at low loads is so great that higher loads must be applied to the Wiper in order to obtain more accurate results. However, at higher loads, Wear on the Wire and the wiper is greater. It will also be seen from the graph thatno such scatter occurs with Wire made from an alloy according to the invention and having a composition 90 Pd=9 I claim:

1. A palladium-vanadium alloy having high specific resistance and reduced temperature coeflicient of resistance, the alloy comprising 74 to 98.5% by Weight palladium, 1 to 15% by Weight vanadium and 0.5 to 11% by weight of at least one element selected from the group consisting of molybdenum and aluminium.

2. A palladium-vanadium alloy according to claim 1 including 15% by weight of vanadium.

3. An alloy according to claim 2 comprising 88% by weight palladium, by weight vanadium and 2% by Weight molybdenum.

4. An alloy according to claim 2 comprising 89% by weight palladium, 10% by weight vanadium and 1% aluminium.

5. An alloy according to claim 2 comprising 90% by Weight palladium, 9% by weight vanadium and 1% by weight aluminium.

6. An alloy according to claim 2 comprising 74 to 98% by weight palladium, 5 to 15% by weight vanadium, 0.5 to 3% by Weight aluminium and 0.5 to 8% by weight gold.

References Cited UNITED STATES PATENTS 2,890,114 6/1959 Ruthardt et a1 172 2,946,679 7/1960 Darling 75134 FOREIGN PATENTS 1,092,212 11/1960 Germany 75- -172 1,092,213 11/1960 Germany 75172 L. DEWAYNE RUTLEDGE, PrimaryExaminer E. L. WEISE, Assistant Examiner U.S. Cl. X.R. 75134 

